I think that it is 64 registers each of 4 different types.

And yes, there was a stack as well, but each item contains a whole set of registers so you only want to do that when you really, really want to. When I saw "was", I'm admitting that I saw the design before they added pervasive continuations to it. I don't know how continuations have changed things, but I know that it isn't a small change.

So the obvious implementation of Forth is pretty much a worst case.

Cheers,
Ben